METHODE POUR ACCROITRE L'EFFICACITE DU BRIS DES GLACES

METHOD OF ENHANCING AN ICE-BREAKING OPERATION

Abrégé anglais

Abstract of the Disclosure.
In order to perform an ice-breaking operation more readily or with a
defined geometry, an ice breaking aid is employed by virtue of which the ice
is irradiated with high-frequency oscillations such as phonons or photons
prior to the ice-beaking operation proper.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of breaking large areas of ice, particu-
larly in the ocean, comprising: (a) selecting a radiation beam
frequency to excite the intermolecular and intramolecular fre-
quency of oscillation in the ice to be broken; (b) irradiation at
least a portion of the ice to be broken with a radiation beam
having said selected frequency, (c) preparing the ice for break-
ing by irradiating said ice in a predefined breakage pattern
forming at least one zone of irradiation, the mechanical proper-
ties of the ice being modified on the surface of the ice with
said at least one irradiation zone thereby reducing the energy
needed to break the ice; and (d) breaking the prepared portion of
the ice.
2. The method as claimed in claim 1, wherein the ice
is irradiated with photons.
3. The method as claimed in claim 1, wherein the ice
is irradiated with photons.
4. The method as claimed in claim 1, wherein the sur-
face of the ice to be broken is irradiated along tracks.
5. The method as claimed in claim 4, wherein the ice is
irradiated over a large area along wide bands.

Description

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The invention relates to a method of enhancing ice-
breaking operations.
Although ice-breakers are employed to keep frozen
regions of the sea open for navigation, there have been hardly
any improvements in the design of such vessels for decades.
Conventional ice-breakers suffer from the disadvantage of a
high power consumption, a low working speed, the possibility
of damage by the ice and relatively poor sailing properties in
the open sea. A substantial advance was made with the intro-
duction of a method based on the principle of shear fracture.
I--lowever this recently developed form of ice-breaking only op-
erates optimally on a restricted ice thickness range and in
limited speed ranges so that if the speed of operation and the
range of application are to be further increased, this system
of ice~breaking may only be used with supplementary ice-break-
ing aids. Mechanical ice-breaking aids have also been pro-
posed, with which the ice is scored and pre-cracked.
The present invention provides a method of afore-
said type which may be undertaken as simply as possible while
at the same time ensuring an effective preparation of the ice
so that it may be more readily and rapidly broken.
In accordance with the present invention the ice is
irradiated with high-frequency waves prior to the ice breaking
operation as such.
In a particular aspect of the present invention a
method of breaking large areas of ice, particularly in the
ocean, comprising: (a) selecting a radiation beam frequency to
excite the intermolecular and intramolecular frequency of os-
cillation in the ice to be broken; (b) irradiating at least a
portion of the ice to be~broken with a radiation beam having
said selected frequency, (c) preparing the ice for breaking by
irradiating said ice in a predefined breakage pattern forming

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at least one zone of irradiation, the mechanical properties of
the ice being modified on the surface of the ice within said
at least one irradiation zone thereby reducing the energy
needed to break the ice; and (d) breaking the prepared portion
of the ice.
The irradiation causes the characteristic properties
of the ice such as the modulus of elasticity, the thrust modu-
lus and the fracture toughness of the ice to be so modified
that predefined breakage patterns result, this then reducing
the energy needed for fracturing the ice in the ensuing break-
lng operation.
The method of the invention furthermore makes lt
possible for ice fragments to be produced with a predetermined
geometry by irradiating along
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the outlines of the desired fragments so that a sort of fracture line or surfaceis predetermined.
The energy used for irradiation is preferably in the form of phonons or
photons as produced by a maser or a laser. Such energy for irradiation
constitutes an aid to ice-breaking that is substantially simpler to apply than
conventional mechanically performed ice-breaking aids.
It is an advantage if the surface of the ice to be broken is irradiated in
a pattern of parallel lines and along predetermined tracks so that the crystal
structure and therefore the mechanical properties of the ice are modified all
over the surface. The strength and the modulus of elasticity of the ice are
this reason further reduced in this zone so that the ice-breaker then moving
through the zone will have to apply substantially less energy. Therefore the
ice-breaker may be also driven through the ice.
There are applications, as for example for research work, in which a
modification of the ice structure that is as homogeneous as possible is
desired. For such a purpose the invention proposes the utilisation of a broad
beam in order to modify the ice in its mechanical properties over a wide area
at a time and therefore achieve an even modification in the structure.
The ice-breaking aid in accordance with the invention is not only
applicable to maritime ice but furthermore to any ice layer (as for example in
the form of a glacier or a frozen mountain lake) that is to be broken.
Figures 1 and 2 are two perspective views of portions of ice sheets that
are to be broken by the method of the invention.
The beam producing device, as for example one in the form of a
high-frequency modulated laser, is moved over the ice 10 in figure 1 along
parallel tracks 11 backwards and forwards. By the use of high-frequency
radiation in a beam 15, whose frequency is so selected that it excites the
inter- and intramolecular frequencies of oscillation in the ice, the structure of
the ice is modified along the zones of irradiation 11 and therefore the strengthis reduced. Accordingly the ice may be more readily broken in the irradiated
zone 12 than in the untreated parts 13.
The double irradiation occurring in the overlapped zones 14 at the edges
of the two tracks of irradiation may cause a further change in structure.
If it is desired to avoid or reduce inhomogeneity in the new structure, a
broad energy beam 15' will be employed that acts on the ice 16 over a wide
area in a single passage.

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A further possible application is the irradiation of single, preset straight I
or curved tracks that function as surfaces of weakness controlling the size and ¦
geometry of the ice fragments to be produced in the ensuing breaking
operation .